Method and apparatus for optically measuring the heating value of a multi-component fuel gas using nir absorption spectroscopy

Abstract

A method and system for measuring heat energy of a combustible fluid in which light having wavelengths in the near-infrared is directed into a test cell containing the combustible fluid and portions of the light not absorbed by the combustible fluid and passing out of the cell are spatially dispersed by wavelength, forming a light spectrum that is projected onto a detector. The light spectrum is digitized and inputted into a data processing unit in which it is compared to the actual spectrum of the light source stored in the system to determine the absorbance spectrum of the combustible fluid. The system is spectrally calibrated by identifying known spectral features of the combustible gas absorbance spectrum. To correct for deviations in the original light source spectrum, a light source calibration system is employed. Upon determination of the absorbance spectrum of the combustible fluid, the heating value of the combustible fluid is determined by comparing the absorbance spectrum to a plurality of spectra located within an on-board database.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to a method and apparatus for the measurement of a physical property of a fluid that is dependent upon a physical characteristic of at least one functional group and is related to the quantity of that functional group in the fluid. More particularly, this invention relates to the measurement of the heating value of a fuel gas at-line and in real time. Even more particularly, this invention relates to a method and apparatus for measuring the heating value of a combustible gaseous fuel mixture, including functional groups and molecules, using near infrared absorption spectroscopy.[0003]2. Description of Related Art[0004]Historically, the heat energy content of a combustible fluid was determined by burning precisely defined amounts of the fluid, e.g. natural gas, to determine the amount of energy produced from the combustion. Other methods determined the concentration of each whole combustible compou...

AI Technical Summary

Benefits of technology

[0011]It is another object of this invention to provide a method and system for measuring the heating value of a fuel gas which embodies quick response times, on the order of less than about 5 seconds, while maintaining initial costs as well as maintenance costs low.

Problems solved by technology

It is difficult to both continuously and accurately measure the energy content of natural gas in pipelines, and the lack of any convenient means for making such continuous and accurate measurements may result in improper charges during the course of a day to the disadvantage of both buyers and sellers.

Commercially, there are no known products capable of accurately determining the heating value of a fuel gas without removing a gas sample and reducing the sample pressure for analysis.

However, such devices, in addition to requiring the removal of samples from pipelines, have slow response times, and have high initial and maintenance costs.

This method of calibration disadvantageously adds a significant amount of time and complexity to the system.

However, the heat of combustion is not measured directly.

However, no means are provided for tracking the fluctuations or degradation of the light source spectrum, which fluctuations or degradation may constitute a large source of error when calculating gas energy content.

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